1. Field of the Invention
The present invention relates to a structure for and a manufacture method of a high-pressure fuel injection tube and, more particularly, to a high-pressure fuel injection tube which has a relatively small diameter such as 20 mm or less and finds wide applications as fuel conduits of a Diesel engine.
2. Description of the Prior Art
In the prior art, the high-pressure fuel injection tube of this kind is generally manufactured, as shown in FIG. 7, by plastically deforming a joint head 12, which has a frusto-conical shape and is formed at each end of an injection tube 11, to give a pressure face 12' by pressing it directly from the outside of its axis with a punch. Incidentally, reference numeral 13 designates a sleeve washer fixed below or on the neck of the joint head 12.
In this prior art, however, the joint head 12 having the direct pressure face 12' on its surface is joined by the (not-shown) fastening nut on the recessed seat of a mating (not-shown) nozzle holder. Especially in case the fuel used has such a low boiling point and a high corrosiveness as alcohol, the pressure face 12' including the leading end face of the joint head is subjected to cavitation erosions or chemical corrosions due to the using conditions including high pressures, vibrations and repeated pressure fluctuations. If, moreover, the joint head 12 is excessively fastened in an eccentric state when it is connected, its pressure face 12' may be scratched so much that a leakage is induced when it is reused after disassembly. Due to the plastic deformation of the joint head 12, still moreover, an annular groove 14 grows deep in the inner circumference of the communication hole 11' in the vicinity of the head, thus raising the problems such as the occurrence of the cavitation erosion or corrosion and an increase in the flow resistance.